1. Field of the Invention
The present invention relates to an electric motor which has an air purge function for preventing entry of foreign matter to the inside of the housing.
2. Description of the Related Art
As this type of electric motor, a spindle motor of a machine tool, in which compressed air is supplies to the inside of a housing from the outside through a tube and the air is discharged from a clearance between the output shaft and the housing is known. This device is described in Japanese Patent Publication (kokai) No. 2007-105850 (JP2007-105850A). However, the spindle motor described in JP2007-105850A requires formation of a flow path of compressed air in the housing, so the housing becomes complicated in structure.
On the other hand, a device is known, in which an air cap is attached at a boundary surface of a spindle and a headstock of a machine tool (an end face of headstock). This device is described in Japanese Patent Publication (kokai) No. 7-299691 (JP7-299691A). In the device described in JP7-299691A, compressed air is supplied to the inside of the air cap and the compressed air inside of the air cap is ejected from the clearance between the air cap and the spindle to the outside of the headstock.
However, in the device described in JP7-299691A, the air cap is attached in a fixed manner to the end face of the headstock, so it is difficult to change the specifications of the device to specifications tailored to situations where no air purge function is required.